Contact lenses are evolving from simple rotational symmetric spherical design for monofocal correction to much more complex design to correct a broad array of visual defects. Aspheric designs provide greater flexibility in correcting aberrations. Rotationally asymmetric lenses, or torics, are correcting astigmatism. Higher order deviations from sphericity and rotational symmetry are now being proposed to go beyond correction to treatment of refractive defects such as myopia. Simple prescriptive parameters of sphere and cylinder are not sufficient for defining the performance of complex refractive correction lens elements.
Optical coherence tomography (OCT) is a well established technique for high resolution volumetric, or tomographic, visualization of translucent materials and biological tissues. OCT is a standard of care in ophthalmic diagnostic imaging, particularly of the retina. OCT systems are generally well characterized for axial or longitudinal resolution. Lateral performance is decoupled from longitudinal performance, and is a function the system optics, including optics of the sample. Precision characterization of lateral and topographic accuracy and precision has not been a requirement for retinal ophthalmology.
Recently, OCT is being studied for characterization of the anterior segment of the eye, and specifically as an adjunct to other topographic diagnostic systems, such as placido rings. With the ability to characterize multiple surfaces in the cornea and the crystalline lens, OCT offers the potential to compute clinical parameters, including refractive power astigmatism, as well as higher order aberrations. Computation of clinical parameters requires an increase in accuracy and precision in both longitudinal and lateral dimensions, as discussed in, for example, U.S. Patent Publication No. 2014/017960 to Egea and U.S. Pat. No. 8,693,745 to Izatt.
The precision required for anterior segment of the eye can be extended to requirements for measuring refractive correction devices for the eye. As the complexity of refractive correction devices increases, there is commensurate need for increased precision in measuring such devices and in computing the clinically relevant parameters for such devices. Refractive correction devices such as contact lenses, corneal inlays and onlays, intraocular lenses, and donor tissues for cornea transplant have material and structural properties that introduce measurement challenges that have not been addressed with anterior segment OCT.